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Mapping the Mars Rovers' Landing SitesContinued...

Setting a Mars Projection

Before plotting the landing site locations, the data frame projection needs to be set. Although a Mars geographic definition will be available in ArcGIS 9, it isn't an option in ArcGIS 8.x. For this exercise, a predefined Mars projection file called Mars_2000Sphere.prj was supplied in the sample dataset. Right-click on the data frame name and choose Properties. Click the Coordinate System tab and select New > Projected Coordinate System. Type in a meaningful name and set the values as shown below in Figure 1.

Projection

Equidistant_Cylindrical

False_Easting

0.0

False_Northing

0.0

Central_Meridian

180.0

Standard_Parallel_1

0.0

Figure 1: Coordinate values

In the lower half of the dialog box, under Geographic Coordinate System, click the Select button and browse to the directory where you unzipped the sample dataset. Choose Mars_2000Sphere.prj and click Add, then click OK to set the projection for the data frame. To use this projection again, click the Add to Favorites button before clicking OK again to close the dialog box.

Plotting the Landing Site Coordinates

The rover locations were determined by the MER navigation and science teams by fitting direct-to-earth (DTE) two-way X-band Doppler and UHF two-way Doppler between the rovers and the Mars Odyssey satellite and matching features in satellite images to images returned from the rovers. With respect to surface features, the Spirit lander is located at 175.4729šE, 14.5692šS, and the Opportunity lander is located in a ~20-meter diameter crater at 354.4734šE, 1.9462šS. These locations are not exact, and as more information is returned, they could change. For this exercise, the Spirit values will be slightly shifted to 175.472636šN, 14.5684šS so they will better fit the images. For additional information on methods for locating the rovers, visit the MSSS site at www.msss.com/mer_mission/finding_mer.

To plot the landing locations, create a text file and name it mer_landing_sites.txt. Type the text in Figure 2 exactly. Save and close this file.

Using the Add Data button, add the file mer_landing_sites.txt to the project.

Right-click on the file name and choose Display XY Data. In the Display XY Data dialog box, set the X Field as the Longitude and the Y Field as the Latitude. Click the Edit button. Before these points can be drawn correctly in an equidistant cylindrical projection, these points need to be defined on Mars.

In the Edit dialog box, click the Select button and browse to the directory where you unzipped the sample dataset. Choose the file Mars_2000Sphere.prj again and click OK twice to exit. Once the file is added, feel free to change the symbol and label options for the map.

After the landing site points are plotted, zoom into the Spirit landing site. Notice the white area under the lander's location. Another white area is northwest of the Spirit lander. The white mark, near the middle of the image, is actually the lander. The northwest white area is the parachute and backshell that detached from Spirit during descent. Also notice the dark scar on the rim of the crater to the northeast. This is believed to have been caused by the impact of the detached heat shield, which was also released during descent.

This image mosaic taken by the panoramic camera onboard the Mars Exploration Rover Spirit shows the rover's landing site, the Columbia Memorial Station, at Gusev crater on Mars. This spectacular view may encapsulate Spirit's entire journey, from lander to its possible final destination toward the east hills. On its way, the rover will travel 250 meters (820 feet) northeast to a large crater approximately 200 meters (660 feet) across, the ridge of which can be seen to the left of this image. To the right are the east hills, about three kilometers (two miles) away from the lander. The picture was taken on the 16th martian day, or sol, of the mission (01/18/19, 2004). A portion of Spirit's solar panels appear in the foreground. Data from the panoramic camera's green, blue, and infrared filters was combined to create this approximate true color image.

The highest resolution image for the Opportunity lander site is called 01_overview_nolabled-B016R1.jpg. This MOC image has a resolution of 1 meter per pixel and contains the white pixel marks showing the lander (left of middle in the small crater) and the parachute and backshell near the western edge. The heat shield scar is in the southeast in the image and directly south of the large crater. This image is courtesy of NAS/JPL/MSSS.

The accompanying illustrations show examples of the final maps for both sites. Have fun exploring the landing site areas and compare these views to images sent from the actual Mars rover landing sites. For more images and information about the Mars rovers, visit marsrovers.jpl.nasa.gov. For planetary GIS information, visit the USGS Planetary GIS support site (aka PIGWAD) at webgis.wr.usgs.gov/.

About the Author

Trent M. Hare, a computer/GIS specialist with the U.S. Geological Survey Astrogeology team since 1994, received a bachelor's degree in computer mathematics from Northern Arizona University. He has also taken additional course work in ArcIMS development, digital photogrammetry, and ArcInfo. He is currently involved in ongoing projects with NASA Planetary Geology and Geophysics, Mars Data Analysis, and other research programs developing GIS Web sites for planetary datasets. His work on the Mars 2003 landing site selection involved writing code specifically designed in ArcView to help generate landing ellipses for targeting the rover's descent. He has also designed and written tools in C++ for photogrammetric and remote sensing software using Viking, Clementine, Pathfinder, and Magellan datasets; created virtual reality modeling language (VRML), image, and DEM importers and exporters as well as provided other USGS projects with GIS and programming support. As part of his work with global 1:1 million datasets, he developed a GIS interface and specialty routines and compiled the datasets. His customized ArcView interface let non-GIS users easily generate maps. He also managed the database creation for a GIS project to compile geologic maps of China. Hare designed the Titan Swath Viewer (TSV) in ArcView for the Cassini satellite and customized the ArcView interface so that novice GIS users could test different satellite targeting scenarios.